The thalidomide disaster of 1958 and later isotretinoin from 1995 showed that drugs do reach the foetus and can cause harm. Even now, of the babies born with a recognised birth defect, drugs are implicated in 1–2%. As a result, there is a perception that any drug at any time in pregnancy could cause harm; however, this is not the case! It’s important to consider the benefit to the mother, the risk to the foetus and the form of administration. This chapter discusses some of the most common drug classes and whether and when they can be safely used in pregnancy.